1. Field of the Invention
This invention relates to an electrophotographic lithographic printing plate precursor and more particularly, it is concerned with an electrophotographic lithographic printing plate precursor excellent in printing adaptability as well as printing efficiency and capable of giving a high image quality print.
2. Description of the Prior Art
Up to the present time, there has generally been employed an electrophotographic process for the production of a lithographic printing plate precursor comprising subjecting the photoconductive layer of an electrophotographic lithographic printing plate precursor to uniform static charge, to imagewise exposure and then to dry development with a dry toner or to liquid development with a liquid toner to obtain a toner image, then fixing this toner image and processing with an oil-desensitizing solution (etching solution) to render hydrophilic a non-image area free from the toner image. The made-up printing plate is fitted to a printing drum and then subjected to printing, during which dampening water is used. As a base for an electrophotographic lithographic printing plate precursor, a paper which has previously been rendered electroconductive, etc. is used, but this paper base is penetrated with the above described etching solution or dampening water during printing, resulting in bad influences on the printing durability, image quality or performances. That is, when the above described etching solution or dampening water during printing penetrates such a base, there arises a problem such as expansion or cutting of a printing plate.
For the electrophotographic lithographic printing plate precursor, therefore, it is required to have the properties as the general electrophotographic light-sensitive material, that is, uniform surface electric property and excellent image forming capacity and developing property as well as environmental stability such as less fogging or less printing unevenness, and moreover, to have the printing properties when used as a printing plate, that is, the water resistance in an oil-desensitizing treatment or to dampening water, organic solvent resistance printing workability and environmental stability.
To this end, it has been proposed to coat the one or both surfaces of a support with, for example, an epoxy resin or ethylene-acrylic acid copolymer having water resisting property (Japanese Patent Laid-Open Publication Nos. 138904/1975, 105580/1980 and 68758/1984) or to provide with a laminated layer of polyethylene or the like (Japanese Patent Laid-Open Publication Nos. 57994/ 1983).
Furthermore, there have been proposed a method comprising providing an opposite surface to a surface of a support having a photoconductive layer (also called "top layer") with a back coating layer (back layer) so as to impart water resistance or to maintain various functions and a method comprising providing an intermediate layer between a photoconductive layer and a precoating layer so as to well maintain both the electrophotographic properties and water resistance (Japanese Patent Laid-Open Publication No. 50465/1990).
When an under layer (undercoated layer) is provided just under a photoconductive layer, however, it is more difficult to stably maintain electrophotographically uniform properties and water resistance with compatibility as compared with the case of using a photoconductive layer alone in the prior art. That is, the electrophotographic properties are affected by the under layer to result in the problems that the toner fogging and light-sensitive property are fluctuated by the environment and in particular, non-image areas of a print produce fishskined toner fogging under low temperature and low humidity conditions. As described above, the surface layer of an electrophotographic photoconductive material is subjected to formation of a toner image and the non-image areas are then rendered hydrophilic by an etching treatment to obtain a printing plate, but it is considerably difficult to allow the surface layer to maintain, with compatibility, both the electrophotographically uniform properties and the water resistance to such an extent that the printing plate does not stretch.
Furthermore, when it is tried to maintain electrophotographically uniform properties in the presence of an under layer, there arises a problem that a hard and brittle support must be used in view of the properties of materials used, resulting in breaking or cutting of a printing plate and springing thereof out of a printing drum. If a tough and flexible material is used for the under layer, electrophotographically uniform stability cannot be obtained, while fogging is increased during developing and fishskined toner fogging appear sometimes.
The present invention has been made to solve the above described problems caused by the provision of an under layer between a support and a photoconductive alyer and just below a photoconductive layer in the electrophotographic lithographic printing plate precursor.